Recent progress in musculoskeletal research has greatly benefited from the advances in molecular biology uncovering the role of specific genes in osteoarthritis (OA). In this gene- centered paradigm, OA pathogenesis results from the lack of appropriate gene expression follow cartilage injury. Therefore inducing the expression of desirable genes is critical. Unfortunately, the absence of a safe and effective gene delivery system has prohibited this approach of gene therapy for articular cartilage repair. LAGeT, LLC has developed a proprietary technology that aims for safe and efficient delivery and activation of a gene of interest in a site- specific manner. This technology, termed light-activated gene transduction method (LAGT), works by irradiating the target tissue with long wave ultraviolet light (UVA) from a laser, thus inducing the host's DNA repair enzymes needed to promote recombinant adeno-associated virus (rAAV) second-strand synthesis. Subsequent rAAV infection of laser-irradiated cells leads to efficient transduction, while non-irradiated bystander cells remain untransduced. Growth/differentiation factor 5 (GDF5) is one of the most promising for gene therapy because it is responsible for chondrogenesis during development. It has been shown previously that GDF5 could be activated in articular chondrocytes within the defect, initiating appropriate repair response. We therefore propose to use GDF5 for validation of LAGT technology. The LAGT technology and supporting in vitro and in vivo data have generated serious interest from the companies specializing in the orthopedics and searching for a delivery system for their genes (i.e. DePuy, Medtronic, Genzyme, Stryker). A consensus opinion has been formed that before LAGT technology is to be licensed or acquired, LAGeT LLC must perform in vivo experiments to demonstrate the commercial potential of LAGT for articular cartilage defects. Therefore, we propose these pre-clinical experiments in a rabbit articular cartilage defects model to: 1) determine the maximum dose of UVA that is not harmful to articular chondrocytes in vivo;2) determine the optimal UVA dose range for laser-activated gene transduction of articular cartilage as defined by the maximal rAAV-eGFP transduction and minimal chondrocyte apoptosis in vivo;and 3) validate laser-activated GDF5 gene therapy of articular cartilage defects in a rabbit model. PUBLIC HEALTH RELEVANCE: Effective gene therapy for tissue repair and regeneration requires site-specific gene delivery to the edge of the damaged tissue. To this end, LAGeT LLC is developing a proprietary technology designed to achieve laser-guided gene delivery. Here we will evaluate the efficacy of this technology in a cartilage model that is relevant to osteoarthritis.